Very high-frequency power generators, such as gyrotrons, which are used for microwave heating, are often operationally coupled with other devices such as a plasma confinement chamber or a sintering chamber. Not infrequently, it happens that the microwave power generator and the device to which it is coupled operate in totally different pressure environments. Typically, as is the case for a gyrotron, the microwave power generator operates in extremely low partial vacuums. On the other hand, the device to which generator is coupled may preferably operate at several atmospheres of pressure. Under such circumstances it is necessary that a pressure (vacuum) barrier be erected between the two. Such barriers are normally referred to as microwave windows.
An important consideration for a microwave window is that, in addition to establishing an effective pressure (vacuum) barrier, it efficiently and effectively allows the transit of microwaves through the window. For this purpose, it is widely known that dielectric materials are preferred. It is also known that, although some dielectric materials are superior to others for transmitting microwaves, even the better dielectric materials exhibit some dielectric losses. Importantly, these dielectric losses include the generation of heat which needs to be effectively dissipated.
One solution for removing heat from a microwave window is to form the window with interior coolant channels which will carry heat from the window during its operation. Several examples of structures for microwave windows which incorporate coolant channels, can be cited. For example, U.S. Pat. No. 5,313,179 which issued to Moeller for an invention entitled "Distributed Window for Large Diameter Waveguides", and which is assigned to the same assignee as the present invention, discloses a vacuum barrier with alternating dielectric and hollow metallic strips. As disclosed by Moeller, a suitable coolant is caused to flow through the metallic strips to cool the barrier. As another example, U.S. Pat. No. 5,548,257 which issued to Caplan et al. for an invention entitled "Vacuum-Barrier Window for Wide-Bandwidth High-Power Microwave Transmission" discloses a device which incorporates liquid-coolant conduits for the purpose of removing heat from the window.
Several competing concerns arise when coolant channels are incorporated into a microwave window. One consideration is that the coolant channels in the microwave window introduces a periodicity which will affect the transmission of microwaves through the window. Unless properly accounted for, this periodicity can cause unacceptable alterations of the wave structure. Further, it is important for the coolant channels to be properly positioned in order to affect the most efficient cooling of the dielectric material in the window. Also, it is necessary that as much power as possible be transmitted through the window. Still further, the structural strength and integrity is affected by the coolant channels.
In light of the above it is an object of the present invention to provide a structural configuration for a microwave window which can be dimensionally designed with an arbitrary thickness to withstand increased pressure differentials across the window, and dimensionally designed with an arbitrary width to accommodate larger microwave power. It is another object of the present invention to provide a microwave window which efficiently removes heat from the window during the passage of microwaves through the window. Still another object of the present invention is to provide a microwave window which minimizes the power that is absorbed by the window during the passage of microwaves through the window. Yet another object of the present invention is to provide a microwave window design which, by tilting the window, allows the window to be scaled for higher frequencies without the need to reduce dimensions of the most difficult to fabricate features. Another object of the present invention is to provide a microwave window which reconstitutes the radiated wave into substantially the same wave structure as that of the incident wave. Another object of the present invention is to provide a microwave window which is easy to use, relatively simple to manufacture and comparatively cost effective.